| 摘要 |
PURPOSE:To vary the gain of an amplifier circuit linearly by adding a collector current detecting circuit and a comparing and amplifier circuit for feedback control. CONSTITUTION:The collector current detecting circuit 13 is connected between the common connection point of collectors of transistors (TR) Q3 and Q4 and a power source +EB. The output of this detecting circuit 13 is applied to the uninverted input terminal of the comparison and amplifier circuit 14. On the other hand, a variable voltage source 7 for gain control is connected to the inverted input terminal of the amplifier circuit 14, and its output terminal is connected to bases of the TRs Q3 and Q4 respectively. Consequently, the TRs Q3 and Q4 are controlled by a voltage corresponding to the difference between both inputs to the amplifier 14 to perform feedback control so that a voltage corresponding to the sum of collector currents of the TRs Q3 and Q4 is equal to the gain control voltage of the voltage source 7. Thus, the gain of the amplifier is varied linearly. |
